TWL1106
VOICEBAND AUDIO PROCESSOR (VBAP)
SLWS094 – JUNE 2001
11
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
power-up initialization
An external reset with a minimum pulse width of 500 ns must be applied to the active-low RESET terminal with
MCLK active to ensure reset upon power up.
Table 1. Power-Up and Power-Down Power Consumption (VDD = 2.7 V, Earphone Amplifier Loaded)
DEVICE STATUS
MAXIMUM POWER
CONSUMPTION
Power-up
16.2 mW
Power-down
81
W
The loss of MCLK (no transition detected) automatically enters the device into a power-down state with PCMO
in the high-impedance state. If an asynchronous power down occurs during a pulse code modulation (PCM)
data transmit cycle, the PCM interface remains powered up until the PCM data is completely transferred.
conversion laws
The device can be programmed either for a 13-bit linear or 8-bit
(-law) companding mode. The companding
operation approximates the CCITT G.711 recommendation. The linear mode operation uses a 13-bit twos
complement format. Linear mode is selected with LINSEL low. LINSEL is high for companding.
transmit operation
microphone input
The microphone input stage is a low-noise differential amplifier. The microphone must be capacitively coupled
to the MICIN– and MICIN+ terminals. Preamplifier (MIC Amp 1) gain is determined by selection of external
resistors R2 and R3. To achieve the recommended gain setting of 23.5 dB for MIC Amp 1, resistor values of
R2 = 34 k
and R3 = 510 k are suggested. A 1% tolerance is recommended for all resistors to meet the
specification. The recommended range for R2 is 34–100 k
. For values above 100 k, the noise performance
of the channel is degraded.
_
+
R3
R2
C1
+V
R1
MICGAIN–
MICGAIN+
MICIN+
MICIN–
MIC Amp 1
R1
+ 2kW
C1
+ 0.22 mF
MIC Amp 1 Gain in dB
+ 20 log R3
R2
Figure 3. Typical Microphone Interface